1. Field of the Invention
This invention relates to the use of selected mixtures of end-capped polyethylene glycol ethers as foam-suppressing additives in low-foaming cleaning products. The invention seeks to provide auxiliaries of the type mentioned which combine high effectiveness with physiological harmlessness and biological degradability. In addition, the invention addresses the problem of, on the one hand, enabling the performance profile of the auxiliaries used in practical application to be optimized and, on the other hand, providing selected polyethylene glycol ethers of the type mentioned which ensure improved formulatability of these auxiliaries in marketable concentrate form. The second of these two aspects is of considerable practical significance as will be appreciated from the following:
Low-foaming cleaning products for institutional and industrial use, particularly for cleaning metal, glass and ceramic surfaces, generally contain foam-suppressing additives which are capable of counteracting unwanted foaming. The foam-suppressing auxiliaries generally have to be used because the soil particles detached from the substrates and collecting in the cleaning baths act as foam generators. However, the cleaning products themselves may contain constituents which give rise to unwanted foaming under the particular working conditions. One example of such constituents are the widely used anionic surfactants.
It is also known that, in industrial cleaning, aqueous acid concentrates and, in particular, corresponding concentrates of aqueous phosphoric acid play an important part as a component of the mixture as a whole. It is desirable in this regard to be able to offer the foam-suppressing additives in admixture with the concentrates. However, reliable and uniform dosing presupposes homogeneous miscibility of the foam-inhibiting components with the aqueous acid concentrates within the temperature range of importance in practice, for example from 0 to 50.degree. C. Separation processes lead to unacceptable phase separation in the active-substance concentrate and thus make it difficult or even impossible to dose the active-substance mixture, particularly in large-scale use. The problem addressed by the present invention is inter alia to provide systems which make improved technical handling possible, particularly in regard to the last of the aspects discussed above.
2. Discussion of Related Art
One class of highly effective and, at the same time, biologically degradable foam inhibitors is described in DE-OS 33 15 951 which relates to the use of end-capped polyethylene glycol ethers corresponding to formula (I) R.sub.1 O--(CH.sub.2 CH.sub.2 O).sub.n --R.sub.2, in which R.sub.1 is a linear or branched alkyl or alkenyl radical containing 8 to 18 carbon atoms, R.sub.2 is an alkyl radical containing 4 to 8 carbon atoms and n is an integer of 7 to 12. A product of this type, wherein R.sub.1 is a C.sub.12-18 fatty alcohol radical, R.sub.2 is the n-butyl radical and n is the number 10, has proved to be particularly successful in practice.
By slightly modifying the structure of the fatty alcohol polyethylene glycol ethers mentioned, it is possible in particular to provide for improved operation at relatively low temperatures, for example of the order of room temperature or only slightly elevated temperatures. DE-OS 38 00 493 relates to the use of polyethylene glycol ethers corresponding to general formula (I) above, in which R.sub.1 is a linear or branched alkyl or alkenyl radical containing 20 to 28 carbon atoms, R.sub.2 is an alkyl radical containing 4 to 8 carbon atoms and n is a number of 6 to 20. In this case, the crucial modification lies in the use of relatively long-chain radicals R.sub.1. These end-capped polyglycol ethers are also distinguished by high stability to acids and alkalis. Their foam-inhibiting effect in alkaline and neutral cleaning liquors is enhanced in the described sense, in addition to which they satisfy legal requirements in regard to biodegradability.
The use of adducts of alkylene oxides with organic compounds containing reactive hydrogen atoms in the molecule as foam-suppressing additives has been known for some time. Those which have been described in the literature include, in particular, adducts of propylene oxide with aliphatic polyalcohols (see, for example, DE-PSS 1 280 455 and 1 621 592) and with aliphatic polyamines (see, for example, DE-PS 1 289 597 and 1 621 593) and also adducts of ethylene oxide and propylene oxide with aliphatic polyamines, more particularly ethylenediamine (see DE-PS 1 944 569). However, compounds of this type are not sufficiently biodegradable to satisfy present legal requirements.